High internal phase emulsions have been known for many years, and have found applications in areas such as food preparation, fuels, oil recovery and cosmetics. Typically, HIPEs are defined as a class of emulsions with a volume fraction of dispersed (internal) phase above 0.74. Examples include mayonnaise, an oil-in-water HIPE with greater than 75% oil droplets suspended in less than 25% external water phase; and Dove® smooth and soft anti-frizz cream, a water-in-oil HIPE with 80% water droplets suspended in less than 20% continuous silicone phase.
High internal phase emulsions are also widely used as a template to create highly porous materials. For example, the internal phase is water and the external oil phase consists of polymerizable monomers. Upon polymerization and removal of the internal water phase a highly porous cellular structure is created. This is widely referred to as PolyHIPE.
In the cosmetic and personal care industry, particles have been widely used in products to provide unique sensory attributes. Biopolymer particles (e.g., agarose, carrageenan) have gained considerable ground, due to their unique properties, as well as to their environmental friendliness or biodegradability.
In a co-pending application U.S. Ser. No. 12/392,646, entitled “Shear Gels and Compositions Comprising Shear Gel”, filed Feb. 25, 2009, applicants disclose shear gel compositions which comprise biopolymer particles prepared in water or polar solvent. These shear gels are prepared by heating a biopolymer/solvent mixture and cooling, with shear, through the gellation temperature of the biopolymer. Particles produced upon cooling or gellation are irregular in shape (e.g., are not predominantly spherical), and have diameter varying from about 1 to 200 microns, preferably 8 to 50 microns. The shearing apparatus comprises a homogenizer operating under a pressure up to 20,000 psi (pounds per square inch), or even up to 45,000 psi.
S. Hjerter (Biochim. Biophys. Acta, 79 (1964) 393-398), discloses a method to prepare spherical agarose particles via suspension-gellation for application in Chromatography. Hot agarose solution is poured into an organic liquid containing hydrophobic stabilizer followed by cooling under agitation. The suspension formed is not a concentrated gel particle suspension and the final suspension contains less than 40% agarose gel. Further, toxic, organic solvents are used in preparation of the suspension and those solvents must be removed. More recently Q-Z Zhou et al (Journal of Colloid and Interface Science 311 (2007) 118-127) reported a preparation method of uniform-sized agarose beads prepared using a microporous membrane emulsification technique. This technique comprises pressing hot agarose solution through uniform-sized pores of the membrane into the oil phase.
Although both methods produced suspensions comprising spherical agarose beads, they have disadvantages in applications in personal care industry and production scale-up. S. Hjerter's method creates a suspension containing less than 40% agarose gel (e.g., is not concentrated as required by suspension of our product). Further, toxic organic solvents must be removed in order to be suitable in personal care industry; filtering/washing of beads increases the process complexity, generates waste and increases cost. Q-Z Zhou's method has issues in scale-up as processes involving microporous membranes generally do. Further, only dilute emulsions (i.e., these are not concentrated suspensions) were reported via the microporous membrane emulsification technique.
The present invention is directed to a process for making novel highly concentrated, spherical gel particle suspensions, wherein a high internal phase emulsion (HIPE) is used as a template or intermediate to create the final concentrated, spherical biopolymer gel particle suspension (i.e., by passing through an intermediate HIPE phase in processing, a novel suspension is formed upon gellation). The final suspension prepared may be used in aqueous or oil based personal care products, or alternatively, gel particle suspensions formed by the process of this invention can be used as is. Both the product formed and the process for forming the gel particle suspensions (HIPE-gelation process) are novel. The process comprises 1) dissolving biopolymer into water or polar solvent (and optional water soluble actives) at elevated temperature to form highly concentrated internal aqueous phase of the HIPE; 2) forming an external oil phase by mixing nonionic surfactant and oils; 3) gradually adding biopolymer solution into the oil phase under moderate agitation (e.g., high pressure homogenization is preferably avoided) to form the HIPE intermediate and 4) cooling the mixture to a temperature below the biopolymer gelation temperature, to form a suspension comprising the concentrated, spherical biopolymer particles of desired size and elasticity. Desired elasticity of particles in the suspension can be manipulated by varying biopolymer concentration used to form the aqueous phase forming the HIPE intermediate (e.g., using 0.01 to 15%, preferably 1 to 10% biopolymer as starting material relative to the aqueous phase). Desired size of particles can be manipulated by choice of oil and or surfactant and or shear through cooling. By this process a suspension can be produced, upon cooling, whereby sensory gel particles can make up 60 to 99% by wt. of the final suspension product. The level of surfactant (having HLB <15, preferably <10, more preferably <7) used in preparation of the HIPE intermediate can be as low as 0.01% by wt. The process may be readily carried out in a general purpose mixer known to those skilled in the art. The particle suspension prepared in this way may be incorporated into an aqueous or oil based personal care product without any destabilizing effects.
The above described process is referred to as HIPE-Gelation process. The process does not require the use of (and preferably avoids use of) high shear devices (e.g. Silverson Rotor-Stator mixer) or high pressure homogenizer, resulting in significant energy saving and savings in capital investment. Furthermore, because the final gel suspension may contain less than 10% by volume nonionic surfactant and oils (used in formation of the HIPE prior to cooling to form the suspension), a high yield of sensory particles (concentrated suspension) is produced. Furthermore, the nonionic surfactant and oils used in forming the HIPE intermediate may be chosen from a range of widely used surfactants and oils in the personal care industry. The suspensions formed from the process are themselves novel in that they comprise highly concentrated, spherical; gel particles suspensions (with some nonionic surfactant and some oil into which particles are suspended). Any composition comprising the novel suspensions prepared by said novel process are, of course, themselves novel.